This invention relates generally to electrical switchgear and more particularly, to a method and apparatus for facilitating optimizing communications between power distribution system components.
In an industrial power distribution system, power generated by a power generation company may be supplied to an industrial or commercial facility wherein the power may be distributed throughout the industrial or commercial facility to various equipment such as, for example, motors, welding machinery, computers, heaters, lighting, and other electrical equipment. At least some known power distribution systems include switchgear which facilitates dividing the power into branch circuits which supply power to various portions of the industrial facility. Circuit breakers are provided in each branch circuit to facilitate protecting equipment within the branch circuit. Additionally, circuit breakers in each branch circuit can facilitate minimizing equipment failures since specific loads may be energized or de-energized without affecting other loads, thus creating increased efficiencies, and reduced operating and manufacturing costs. Similar switchgear may also be used within an electric utility transmission system and a plurality of distribution substations, although the switching operations used may be more complex.
Switchgear typically include multiple devices, other than the power distribution system components, to facilitate providing protection, monitoring, and control of the power distribution system components. For example, at least some known breakers include a plurality of shunt trip circuits, under-voltage relays, trip units, and a plurality of auxiliary switches that close the breaker in the event of an undesired interruption or fluctuation in the power supplied to the power distribution components. Additionally, at least one known power distribution system also includes a monitor device that monitors a performance of the power distribution system, a control device that controls an operation of the power distribution system, and a protection device that initiates a protective response when the protection device is activated.
In at least some other known power distribution systems, a monitor and control system operates independently of the protective system. For example, a protective device may de-energize a portion of the power distribution system based on its own predetermined operating limits, without the monitoring devices recording the event. The failure of the monitoring system to record the system shutdown may mislead an operator to believe that an over-current condition has not occurred within the power distribution system, and as such, a proper corrective action may not be initiated by the operator. Additionally, a protective device, i.e. a circuit breaker, may open because of an over-current condition in the power distribution system, but the control system may interpret the over-current condition as a loss of power from the power source, rather than a fault condition. As such, the control logic may undesirably attempt to connect the faulted circuit to an alternate source, thereby restoring the over-current condition. In addition to the potential increase in operational defects which may occur using such devices, the use of multiple devices and interconnecting wiring associated with the devices may cause an increase in equipment size, an increase in the complexity of wiring the devices, and/or an increase in a quantity of devices installed.
Centrally controlling of power distribution systems may overcome the above mentioned shortcomings of known power distribution systems. Central control systems may also present new problems which may need solutions before central control systems become a viable new control system. For example, communications between the central controller and controlled devices may occur over long distances, redundancy requirements may make communications slow due to additional devices communicating in parallel, and separate communication channels may need to be cross-checked for accuracy.
Central control systems may receive electrical inputs from the controlled process through remote input/output (I/O) modules communicating with the central control system over a high-speed communication network. Outputs generated by the industrial controller are likewise transmitted over the network to the I/O circuits to be communicated to the controlled equipment. The network provides a simplified means of communicating signals over an industrial environment without multiple point-to-point wires and the attendant cost of installation.
The central control system may use real time control to achieve latency goals. Effective real-time control is provided by executing the control program repeatedly in high speed “scan” cycles. During each scan cycle each remote node samples inputs at a selectable frequency and output messages are computed. The output messages are transmitted to the central control location where these data samples are processed to provide a control of the system such as centralized control. A relatively large number of samples are taken at the remote node, such as, for example 128 samples per second, and are packaged to share space in a message. Together with the high-speed communications network, this ensures the response of the central control system to changes in the inputs and its generation of outputs will be rapid. All information is dealt with centrally by a well-characterized processor and communicated over a high-speed communication network to yield predictable delay times, and low latency, which is critical to deterministic control. The high data transmission rate and large number of remote nodes attempting to communicate creates network traffic congestion that may adversely affect power distribution system latency and the ability of the power distribution system to operate efficiently.